Crystallography, materials and computation

The birth of crystallography 100 years ago was in the determination of the structures of inorganic materials. And materials continue to pose some of the most fascinating challenges in our discipline. Moreover, structural studies in materials science and indeed in all areas are increasingly supported by computation which now permeates all aspects of crystallography

Challenges in the structural science of materials

Articles published recently in IUCrJ continue to exemplify the developments and challenges in the structural science of materials

Computational investigation of CO adsorbed on Aux, Agx and (AuAg)x nanoclusters (x = 1-5, 147) and monometallic Au and Ag low-energy surfaces

Density functional theory calculations have been performed investigating the use of CO as a probe molecule for determining the structure and composition of Au, Ag AuAg nanoparticles. For very small nanoclusters (x = 1-5), vibrational frequencies can be directly correlated to CO adsorption strength, whereas larger 147-atom nanoparticles showed a strong energetic preference for CO adsorption at a vertex position but the highest wavenumbers are calculated for the bridge positions. We also studied CO adsorption on Au and Ag (100) and (111) surfaces, for a 1 monolayer coverage, and this proves to be energetically favourable only on atop and bridge positions for Au (100) and atop for Ag (100); vibrational frequencies for the CO molecule red-shift to lower wavenumbers as a result of increased metal coordination. We conclude that vibrational frequencies cannot be relied upon solely in order to obtain accurate compositional analysis, but we do believe that elemental rearrangement in the nanocluster from Ag@Au (or Au@Ag) to an alloy would result in a shift in the vibrational frequencies that indicate the change in the surface composition

Recent developments in the structural science of materials

This Editorial surveys the current status and recent developments in the structural science of materials as exemplified by the articles recently published in IUCrJ

Computational Techniques

This chapter introduces fundamental computational approaches and ideas to energy materials. These can be divided into two main streams: one dealing with the motion of atoms or ions described at a simplified level of theory and another focusing on electrons. The modeling framework, which covers both streams, is outlined. The atomistic simulation techniques discussed in the chapter are concerned with describing the energy landscape of individual atoms or ions, where classical mechanics can be usefully employed as the first successful approximation. Multiscale approaches could be the method of choice if one is interested in large molecules, inhomogeneous solids, complex environments or geometrical arrangements, systems that are far away from equilibrium or have particularly long evolution times. One of the principal objectives of atomistic simulations is to derive an accurate and coherent approach to the prediction of defect structure, energetics and properties. Two of the most widely employed methods are outlined. This edition first published 2013 © 2013 John Wiley & Sons, Ltd

Neutron spectroscopy as a tool in catalytic science

Catalytic science currently has access to a range of advanced experimental methods for the study of molecular behaviour in chemical processes. Neutron spectroscopy, however, is uniquely placed to gain detailed insight into such systems, particularly through techniques such as vibrational spectroscopy with neutrons (INS) which gives access to vibrational modes unavailable to conventional spectroscopy techniques, and quasielastic neutron scattering (QENS) which studies molecular motion on a range of timescales. The present article illustrates the role of these techniques in advancing the field of catalysis. We first provide a brief introduction to the basic principles of the techniques, and then discuss their use in the study of three key catalytic systems: the behaviour of hydrocarbons confined in zeolite catalysts; the methanol-to-hydrocarbons process; and methane reforming. We demonstrate the importance of neutron spectroscopy in understanding established catalytic processes, but also consider its role in the design of future catalytic systems